Paternal behavior within the system of biparental care by the California mouse, Peromyscus californicus, will be analyzed from a novel perspective that combines new studies of triadic interactions with the analysis of resource exchanges among parents and offspring. Maternal behavior in this species will also be examined systematically. Basic studies are proposed to: (a) provide normative profiles of paternal and maternal care from birth of young to weaning, (b) examine mechanisms underlying the prepartum onset of paternal behavior, and (c) determine the influence of the mother and offsping on postpartum maintenance of paternal behavior. Body water, electrolytes, and heat are "primary metabolic commodities" that are actively exchanged among family members. Water recycling via pup urine, its effects on parental body fluid balance, and its use as a fluid substitute by both parents will be examined. We shall also study development of thermogenesis, effects of parental heat on the young and patterns of bidirectional, heat transfer between parents and offspring. The contribution of the male's presence to the growth, development, weaning, and sexual maturation of his offspring will be determined.